Touchpads are coordinate type pointing devices used to input coordinate type data to computer systems and computer-controlled devices. A touchpad is typically a pressure-sensitive bounded plane capable of detecting localized pressure at its surface. When a user touches the surface with a finger, stylus, or the like, the circuitry associated with the touchpad determines and reports to the attached computer system the coordinates of the location touched. In response, the computer performs the function, if any, associated with the location pressed.
Typically one or more regions of the touchpad are assigned to certain functions within the system. The user is made aware of what function is associated with each region by a template. A template is a sheet with a graphic design and is typically placed over and in contact with the touchpad surface. The graphic design typically maps out regions of the touchpad surface and the regions are typically labeled to provide a reminder to the user as to the functions associated with the various mapped regions.
A touchpad's sensor is the heart of the touchpad. Several types of touchpad sensors are known in the art, such as switch closure type sensors. For example, a keyboard sensor having matrix of membrane switches is disclosed in U.S. Pat. No. 4,736,190 to Florella. A touch by a finger on a key causes a closure event between a pair of conductors. As with other switch closure type sensors, the location of the touch is detected using a bank of digital signal drivers and a bank of digital signal receivers.
Other devices known in the art are very complex. For example, U.S. Pat. No. 4,529,959 to Ito et al. discloses a sensor for a coordinate type input device comprising a braided lattice of conductors embedded in a compressible open-cell insulating material sandwiched between two insulating layers coated with a resistive material. Complex devices such as the Ito et al. device can be difficult and expensive to manufacture.
Another sensor is shown in U.S. Pat. No. 4,455,450 to Margolin. This sensor involves resistive sheets sealed into a "pillow" form. Critically, the pillow is filled with a pressurized fluid, which prevents contact of the resistive sheets. Being pressurized, the seal between the sheets must be maintained or the sensor might depressurize. Such a depressurization would allow the sheets to come into contact, thereby causing an electrical short circuit between the sheets, rendering the sensor useless.
It is therefore desirable to provide a reliable high-density switch closure type touchpad sensor that is readily manufactured.